IETF has standardized IEEE802.11s (multi-hop relay based on IEEE 802.11) as a protocol for enhancing transmission and reception efficiency with respect to coverage and energy of IEEE 802.11. In addition, in a similar way, it has also standardized IEEE802.16j employing the multi-hop relay of IEEE802.16.
Based on the multi-hop relay, signals can be transferred even outside the region of a base station through a relay station (RS), and a terminal within the region of the base station may set a path of high quality having a high-level adaptive modulation and coding scheme through the relay station, and thus system capacity can be improved using the same wireless resources.
However, since such a multi-hop situation has link dependency among adjacent routing nodes due to sharing of wireless channels for transmitting data, throughput starvation occurs, in which throughputs of some flows are extremely lowered.
Furthermore, probability of congestion occurring is high in a network which frequently changes depending on a wireless channel state. Accordingly, it is impossible to flexibly adjust and improve fairness in a conventional method of adjusting a transmission rate by monitoring only own flow state.
For example, a distributed scheduling technique for controlling a transmission rate among distributed end points has been proposed in the prior art in order to prevent the throughput starvation.
In such a distributed scheduling technique, an end node directly or indirectly monitors a state of a network path through which its own flow passes, instead of information regarding the entire network, and determines a transmission rate based on the monitored information in order to control its own transmission rate. Particularly, a flow having a low throughput tries to obtain higher throughput by continuously increasing its own transmission rate in order to increase fairness.
Accordingly, the distributed scheduling technique is a problem of determining a sequence of communication with adjacent nodes in the nodes configuring the network.
At this point, the nodes try to increase fairness by solving the problem of throughput starvation in a method of monitoring states of geographically close nodes and granting a higher communication priority to a flow which obtains a low throughput based on the monitored states.
However, such a method does not work based on the information regarding the entire network. Accordingly, the determination is wrong in many cases due to limited amount of information, and thus there is a problem in that a high fairness is not demonstrated.